1. Field of the Invention
The present invention relates to a vehicular lamp provided with a projector-type lamp unit.
2. Background Art
In the projector-type headlamp 200 shown in FIG. 11, for example, a light source 204a of a light source bulb 204 is disposed in proximity to a first focal point of a reflector 203 having a rotational ellipsoidal surface, and a bilaterally symmetrical projection lens 202 having a rear side focal point is disposed in proximity to a second focal point at which light from this light source 204a converges. In this type of conventional projector-type headlamp 200, the light emitted from the light source bulb 204 converges once at the second focal point, and subsequently the light that diffused in a radial fashion is projected in the radiation direction by the projection lens 202.
When using the reflector 203 having a rotational ellipsoidal surface, light reflected at the reflector 203 is condensed in proximity to the rear side focal point of the projection lens 202, and the light that is refracted and emitted by the projection lens 202 is projected forward in a condensed state as a substantially parallel light flux. Such a reflector 203 is used, for example, in a high beam lamp unit, and can radiate light a long distance. However, in this type of reflector 203 having a rotational ellipsoidal surface, because the light cannot diffuse sufficiently in the horizontal direction, the sideways visibility is relatively reduced.
A technique for enhancing the sideways visibility, as shown in FIG. 12, is a projector-type headlamp 300 that uses a reflector 303 and a bilaterally symmetrical projection lens 302, where the reflector 303 is provided with a reflecting surface having a cross-sectional profile on the optical axis Ax that is generally ellipsoidal in shape, and an eccentricity thereof is set so as to increase gradually from a vertical cross-section to a horizontal cross-section, that is, a vertical cross-section has a generally ellipsoidal profile and the horizontal cross-section has a free-form surface profile based on an ellipse. See, e.g., Japanese Patent Application Publication No. JP-A-2001-76510.
In the projector-type headlamp 300, in particular in the horizontal cross-section, because the reflector 303 is designed such that the light rays from the light source 304a of the light source bulb 304 are reflected forward beyond the rear side focal point of the projection lens 302 so that their distance from the optical axis increases, the light diffuses in the horizontal direction, and it is possible to enhance the sideways visibility.
However, when using the reflector 303 having a reflecting surface whose vertical cross-section has a generally ellipsoidal profile and whose horizontal cross section has a free-form surface profile based on an ellipse in order to increase the diffusion in the horizontal direction, it is not always possible to accommodate the sharp slant of a cover 305 along an external contour of a vehicle body. As shown in FIG. 12, a portion of the diffused light emitted from the light source 304a and radiated toward the inside of the vehicle may be blocked by the extension 306 or the like.
In order to prevent the diffused light from being blocked in this manner by the extension, narrowing the diffusion angle of the light in the transverse direction of the vehicle may be considered, but in a bilaterally symmetrical optical system, because the left and right diffusion angles are identical, there is a problem in that the diffusion angle toward the outside of the vehicle is reduced when the diffusion angle toward the inside of the vehicle is reduced. In such a structure, there is a concern that the nighttime sideways visibility will decrease and bring about a deterioration in safety. In addition, in a conventional bilaterally symmetrical lens, the light incident on the outer peripheral portions of the lens toward the inside of the vehicle is reflected by the lens emitting surface, and as a result, the light utilization rate decreases, and the diffused light that is radiated toward the outside of the vehicle decreases.